Session Index

Light emitting diodes (LEDs) are the emerging next generation lighting technology but obtaining high performance green and longer wavelength LEDs, require InGaN alloys with higher indium content has proven difficult. One major problem is that the lattice mismatch between InGaN active quantum wells and the surrounding GaN layers worsens with increasing indium content. In addition, localization mechanism associated with compositional fluctuations that allow bright LEDs in the blue is no longer valid. In this work ZnO substrates are used for GaN and InGaN growth by metalorganic chemical vapor deposition (MOCVD). ZnO offers many advantages for GaN and InGaN due to its closely matched lattice constant, similar thermal expansion coefficients, and its ability to also be easily chemically etched, which results in improved light extraction. However, H2 etching of the ZnO substrate at high temperatures, Zn diffusion out of the substrate, and the stability of an oxide substrate in a highly reducing atmosphere still cause many issues during MOCVD growth. The direct nucleation of GaInN on ZnO is considered in this work including some native and non-native III-Nitride transition layers. The transition layer was grown on the substrates before or during the MOCVD growth to prevent Zn diffusion, protect the ZnO substrate from H2 back etching, and promote high quality nitride growth on the ZnO substrates. It was found that Al2O3 grown by Atomic Layer Deposition (ALD) on ZnO was a particularly effective transition layer. High resolution x-ray diffraction (HRXRD) measurements revealed that the thin Al2O3 layers after optimal annealing showed distinct wurtzite GaN and InGaN films grown epitaxially on ZnO with a mirror-like surface, no etched pits, and no peeling off. This work was extended to LEDs grown on Si with an ALD Al2O3 transition layer and these devices had a turn on voltage of <5V.

 

Confocal Raman spectroscopy is adopted to analyze strain distribution of GaN layer on patterned sapphire substrate. The Raman mapping results show that strain distribution is strongly correlated to the pattern on sapphire substrate.

 

We simulated AlGaN-based UVC LEDs with alloy fluctuation model. The alloy fluctuation model helps to form a permeation path for carrier injection, but also reduces carrier confinement within the quantum wells. The extension of the wave function into quantum barriers enhances TM emission, which might lead to poor light extraction.

 

Green InGaN-based LED with an embedded nanopipe GaN layer was demonstrated. The EC-etched pipe structure can be observed through the electroluminescence emission images through a polarizer. The polarized EL emission light with 537nm and 558nm peak wavelengths was observed in the EC-LED.

 

Abstract: 20 pair n-type GaN:Si/undoped-GaN stack structure were transformed into the porous-GaN/u-GaN distributed Bragg reflectors (DBR) structure through the doping-selective electrochemically etching process. Polarized reflectivity and central wavelength of the porous GaN DBR were measured as the values of 93.8%/440nm perpendicular to the pipe and 93.0%/465nm along the pipe structure.

 

286nm AlGaN-based UVC light-emitting diodes (LED) with an embedded nanoporous AlGaN layer was demonstrated. The n-type AlGaN:Si layer was transformed into the conductive porous AlGaN layer with triangle-shaped air void structure through the electrochemical wet etching process. Far-field radiative patterns of the TE- and TM-modes EL spectra were analyzed.

 

MicroLED display is believed to be the next generation of flat panel display. The concept of MicroLED display is simple. It can be considered as an LED video wall but shrunk into consumer product sizes with micro-meter scale LED chips as sub-pixel emitting elements. The reasons to develop MicroLED display are lower energy consumption and better environmental reliability. Current LCD is a light absorbing device, which means most of light from backlight unit is wasted and transformed to heat. This will be a big energy crisis while we use more and more displays. OLED seems can reduce some energy consumption as an emissive display, but it is limited by material lifetime and weak environmental reliability. MicroLED could be a good solution by highly efficient inorganic LED chips. MicroLED display can meet all requirements for high performance display. It can achieve ultra-high resolution, ultra-low power consumption, high brightness, flexible display with any shape, fast response time, and good environmental reliability. MicroLED is the only display technology can fulfill high display quality standard, and we believed MicroLED will be the ultimate display technology. By using PlayNitride proprietary PixeLED® display technology, we have built 3.12” 256x256 pixels and 5” 320x160 pixels full color MicroLED sample. This sample was built by passive matrix backplane, red, green, and blue MicroLED chips, and a passive matrix OLED driver IC. Both displays are transparent with more than 50% transmittance, and high brightness more than 800 nits. MicroLED display is an emerging technology with high brightness, wide color gamut, and high aperture ratio. In additional to traditional display applications, MicroLED display can be used for innovative display technology. Based on our proprietary PixeLEDTM Display technology, we demonstrated two MicroLED displays which can show the ultimate display performance.

 

CdSe/ZnS quantum dots (QDs) and poly(N-vinylcarbazole) polymer material were used to fabricate the emission layer of inverted white organic light-emitting diodes (WOLED). Furthermore, an ITO nanorod with period of 1.5 µm was added. The maximum efficiency was improved to 3.12 cd/A and the CIE of the WOLEDs was (0.329, 0.331).

 

We proposed a lighting lens design with an optical efficiency of 77.6% and optical utilization factor at the region of 36 m × 21 m above 60%. Therefore, the proposed luminaire not only fits the geometrical shape of the sport field but also the regulation of international sport field.

 

To solve the fast anion-exchange phenomenon and further reduce quantum dots(QD) self-aggregation, We used red CdSe/ZnS QD and green perovskite QD to fabricate liquid-type white LED, which achieve outstanding performance of high luminous efficiency, wide color gamut, and high stability.

 

Our study shows contradictory results of the adoption of gate field plates for suppressing current collapse. At the low off-state drain bias, current collapse is deteriorated with the additional gate capacitance. At higher voltage, the effect of gate field plate takes in by re-shaping the vertical electric field distribution.

 

In this study, the Si and Ti co-doped n-type GaN films with ZnO buffer layers were grown by using the sputtering technique on amorphous glass substrates. The Hall measurement results show that Si-Ti co-doped n-type GaN can reduce resistivity of GaN film to 2.63×10-1ohm-cm with carrier concentration of 4.58×1019cm-3

 

In this study, p-type GaN films were deposited by Mg-Zn co-sputtering with a ZnO buffer layer on amorphous glass substrates. The results of XRD and PL measurements show that the thin films were grown along with c-axis (002) direction with high crystalline quality.

 

The electric modulus (M) spectroscopy was employed to characterize the electrical properties of InGaN/GaN multiple quantum well light emitting diodes. The result showed that we found two main junctions in the device which can be identified as the main active junction and the heterojunction between the AlGaN EBL and p-GaN.

 

This research presents a silicon via backend process for AlGaN/GaN-on-Si platform-based devices. The DC characteristics, dynamic measurements and thermal performances are compared between devices with and without backside via. A model proposed was involved into the explanation of heat dissipation mechanism and relation between DC characteristics and thermal effect.

 

In this investigation, a p-type Mg/Cu co-doped GaN film was grown by a cosputtering technique at 500°C and 600°C on an amorphous glass substrate with a ZnO buffer layer. In addition, relevant material analyses such as XRD, PL, XPS, and Hall measurement were performed, and they are described herein.

 

In this paper, the Si-Sn co-doped n-type gallium nitride (GaN) films were grown with ZnO buffer layers on amorphous glass substrate by sputtering deposition system. The Hall measurements of Si-Sn co-doped n-GaN film has a low resistance of 1.71×10-1 ohm-cm with high carrier concentration of 1.84×1019 cm-3

 

The optimal white LED spectra for mesopic lighting condition which are able to raise the mesopic luminance and also expand the range of 3D color gamut with satisfying color rendering indices were discussed. The results suggest that the optimization of trichromatic white LED spectra needs intensive study.

 

The optimal LED spectra for the highest CRI of any CCT are obtained. By an empirical spectral function specifying the LED spectra with high accuracy, the optimal LED spectrum can be easily evaluated. Therefore, a series of the optimal LED spectra for the highest CRI of various CCTs is concluded.

 

"Solution-processed organic-inorganic metal-halide perovskites have been considered as an alternative material for the cost-effective and large-scale manufacturing in variety of optoelectronic devices [1]. Moreover, several advanced researches recently indicate that the perovskites show excellent material properties such as the promising photoluminescence (PL) quantum efficiencies exceeding 70 % and broad emission spectra covering most of the visible range with compositional adjustment, making them feasible for efficient on-chip coherent light-emitting devices [2]. Despite many laser cavities have been proposed to support the lasing action of perovskites from different fabrication processes, for example, crystalline microcavity, nanowire cavity, vertical cavity with both dielectric coated DBRs, and thin film cavity with surface grating, perovskite thin film itself exhibits the random lasing performance even without any resonant cavity. We are the first few groups that demonstrated random lasing behaviors from the solution processed CH3NH3PbI3 thin film at low temperature and reported the phase transition behavior [3]. We also observed the effect of nano-crystalline structures existed in the perovskite thin films on the performance of lasing process [4]. In order to further increase the operation temperature, we applied plasmonic structures on the perovskite thin film to further improve the laser performance by employing the stronger interaction between light and perovskite gain medium [5]. Recently, we exploited the novel solvent-engineered method to make solution-processed methylammonium lead bromide perovskite thin films with excellent optical properties. The random operation can be easily observed at above room temperature condition. Furthermore, with the perovskite synthesized on flexible polyimide (PI) substrates, the lasing performance can be actively controlled via the bending modulation of the supporting substrates, offering a new route to develop the wearable optoelectronic devices. Finally, we applied this random laser light source for the imaging of a simple double-slits system and AF resolution test chart. The acquired low spatial coherence and high contrast-to-noise ratio indicate that such a perovskite thin film random laser can be applied for the advanced speckle-free imaging [6]."

 

We have proposed a highly efficient solution-processed organic light-emitting diode (OLED) with low turn-on voltage based on PEDOT:PSS/TAPC as a hybrid hole injection and electron blocking layer. The best-performing device with the resultant HIL exhibits superior performance (CE=40.1 cd/A, Von=2.7 V) than with PEDOT:PSS (CE=35 cd/A, Von=3 V) at 1000cd/m2

 

In this study, we propose a methodology to enhance the lifetime of flexible organic light-emitting diodes (FOLEDs). By means of improving the encapsulation on FOLEDs, we can increase the efficiency of thermal dissipation. Graphene is the main material to achieve our expected result because of its high thermal conductivity

 

Solar-like light in the wavelength range of 450-650 nm is achieved by LED light source improved by optical filter, which have invert spectrum of the LED light. The filters have about 30 multilayer films fabricated by optical coating. The filtered light has high color rendering rate of 95.6 for D65.

 

In this study, we propose high-performance lead-free perovskite light-emitting diodes based on low-temperature solution-processed lead-free per-ovskites.

 

This study is to use dry etch,wet etch and light extraction layer methods to rough the light emitting surface (p-GaP) of the red LED to reduce the internal total reflection phenomenon of the LED to increase the light output rate.

 

Quantum dots light-emitting diodes (QLEDs) based on MoS2 QDs have been demonstrated. Exhilaratingly, we have succeeded in fabricating the low-toxic white light emitting diodes which have not been done so far. This work may open the route for using transition metal dichalcogenides (TMDs) QDs as light emitting devices.

 

In this study, we introduce new process of partially alignment liquid crystal modulator used in the tuning the correlated color temperature (CCT) of white light-emitting diodes (LEDs). The liquid crystal modulator with partially alignment is realizing a CCT-tunable white light whose CCT can be accurately controlled.

 

In this article, we investigate the optical frequency response of GaN-based blue LED with and without electron retarded layer (ERL). The EQE with ERL were improved 9.15 % with ERL, however the optical frequency response decay decreases seriously due to the poor electron transport caused by ERL structure.

 

Deep-red Mg2TiO4:Mn4+ phosphor was synthesized by solid-state reaction at 1300°C for 5 h. The influence of Mn4+ concentration on the luminescence properties of phosphor was discussed. Under UV and blue light excitation, Mg2TiO4:Mn4+ exhibited red luminescence at wavelengths 661 and 677 nm, which is potential for white light-emitting diode application.

 

A novel p-electrode design for AlGaN deep ultraviolet light-emitting diodes (DUV-LEDs) is proposed. The 9-finger-design DUV LED exhibits higher light output power, external quantum efficiencey and better current spreading uniformity. A 1.65 mW at 20 mA is obtained corresponding to a performance enhancement of 154% compared with others DUV LEDs.

 

The p-up GaInP thyristor has an ITO window layer can increase the output power of 497% and reduce the turn-on voltage of 0.74 V. But the n-up AlGaAs thyristor has an ITO window layer only increases the output power of 21% and increase the turn-on voltage of 6.19 V.

 

We demonstrate inverted perovskite light-emitting devices based on ZnO nanocrystals and cesium lead bromide film as the electron injection and emission layers, respectively. Furthermore, polyethyleneimine ethoxylated and an ionic polyfluorene derivative containing trimethylammonium hexafluorophosphate groups were introduced as the electron transport bilayer to enhance device performance.

 

We report that the optical microcavity/Purcell effect, in addition to enhancing light extraction, can also be judiciously used as an additional/independent approach for boosting the radiative transition rates/emission quantum yields of thermally activated delayed fluorescent emitters in devices particularly for the spectral ranges more difficult for high emission quantum yields.

 

Fluorescent substrates have been fabricated for white organic light-emitting diodes (WOLEDs). Phosphor crystals have been embedded into the glass substrates for the color-conversion function. The photoluminescence and photoluminescence excitation of the substrates have been studied in this work. The substrates can be used as color down-conversion substrates to realize WOLED.

 

The photometric characteristics of LEDs during their accelerated aging processes are explored extensively. One empirical model to describe the aging process of LEDs is proposed. Sixty LED chips are monitored on their normal operation to failure. Then, four aging characteristics of LEDs are found and analyzed.

 

In this paper, a spectral calculation method which can simply and directly evaluated by the weight of phosphor is developed to predict the spectral changing that the blue light emitting diode coated by the two-colors mixing phosphors.

 

The β-Ga2O3 thin films were grown on (001) LiGaO2 by hydride vapor phase epitaxy (HVPE). The effect of low temperature buffer layer on the growth of Ga2O3 film was investigated. The crystal orientation relationship is [001]LGO || [-201] β-Ga2O3, [100]LGO || [010] β-Ga2O3 and [010]LGO || [102] β-Ga2O3.

 

To provide a planar light source using laser-driven white light, a planar light guide design with remote phosphor layer is used in this study. The laser from LDs undergoes total internal reflection (TIR) and hits the remote phosphor on the planar light guide to generate the white light.

 

To realize the laser-based white light technology, the ring remote phosphor structure is used in this study. The inverted cone lens encapsulant in the structure directs the light from the blue laser diodes (LDs) to the surrounding phosphor layer, and reduces the high density laser irradiation on the phosphor layer.

 

The effect of annealing on AlN crystal grown by MOCVD is studied. It is found the annealing under the condition of 1180 C and pulsed NH3 flow can effectively improve surface morphology and lattice quality of AlN epilayer. Details of characterization will be provided.

 

OLEDs possess many outstanding characteristics, such as high efficiency, low power consumption, fast switching, and has evolved to the extent that commercial applications for cell-phones, televisions and lamps are available, photoluminescence, a powerful and breakless analysis technology, can reveal the band structure and the carrier transportation behaviors in a material.